After the court proceeding, Senator Estrada said President Benigno Aquino was not serious about fighting graft but was persecuting the political opposition

(Corrects spelling of word in paragraph 5)

MANILA June 30 (Reuters) - A Philippine lawmaker, the son of a former president ousted in 2001 on corruption charges, refused to enter a plea on Monday on charges he plundered $4.2 million from his congressional fund, saying the charges were politically motivated.

Jose "Jinggoy" Estrada, an action movie hero-turned senator and eldest son of former president and now Manila mayor Joseph, stood silently in the court when the charges were read out.

One of the three judges then entered a plea for opposition senator Estrada of "not guilty". Estrada faces life imprisonment if convicted for plundering more than 183 million pesos ($4.20 million) from his congressional funds from 2004 to 2010

After the court proceeding, Estrada said President Benigno Aquino was not serious about fighting graft but was persecuting the political opposition.

"The Ombudsman haphazardly filed an information before the Sandiganbayan... without strong evidence against me," said Estrada, reading a statement, referring to the anti-graft court.

"This also further bolsters what I've been saying all along that this is politically motivated with no other intent but to persecute the members of the opposition while protecting their allies."

In 2010, President Benigno Aquino won the presidency on the platform of good governance and transparency, with plunder cases are central to his effort to shed the country's image as one of the most corrupt in Asia.

But he has failed to wipe out graft in government and has been increasingly under attack for coddling political allies accused of corruption.

Prosecutors had tried to amend the charges against Estrada to show he was "collecting" and not merely "receiving" kickbacks from a businesswoman who allegedly devised the scheme to divert congressional funds to non-existent non-government organisations implementing agricultural projects.

But they withdrew their motion when the court denied it.

Estrada said prosecutors filed a defective case against him and believed the court should grant him bail to walk free from the police camp where he has been held for a week.

Two other opposition senators are facing similar plunder charges, one has been arraigned and another, a 90-year-old, is appealing to avoid detention due to his old age and poor health. Prosecutors said the senators had siphoned of funds, known as "pork barrel", to non-existent non-government organizations. ($1 = 43.6150 Philippine Pesos)